Norway Rat

Description

The Norway rat is a large rodent with short, coarse fur that is
grayish-brown above and pale below. It weighs 280-540 grams (10-19 oz) and
measures 30-50 cm (12-19 in) long including a 15-23 cm (6 -9 in) tail that is
covered with scaly rings. This species is differentiated from the Eastern
woodrat by its scaly tail and smaller eyes.

Habitat and Biology

The Norway rat is widespread throughout all of North America. It frequents
diverse habitats such as salt marshes, wharves, garbage dumps, and sewers.
However, this rat can be found anywhere it finds shelter and a food source.
Since its introduction in the eighteenth century, it has spread prolifically
throughout the United States.

The Norway rat is polygamous, breeds year round, and lives up to 3 years in
the wild. It produces an average of seven litters per year with 7 to 11 young
per litter. Gestation in this species lasts 21-23 days, after which the female
gives birth to altricial young (naked and blind) who open their eyes after
approximately 2 weeks. Young are weaned at 3 weeks and are ready to reproduce
after approximately 4 months. Norway rats construct their nests out of rags,
paper, or other suitable material. Colonies typically consist of 10 to 12
individuals with one dominant, older, larger male.

Norway rats consume almost anything organic they can find and have been
known to kill poultry, birds, and rabbits. They are themselves important food
for raptors, snakes, and predatory mammals.

In the late eighteenth century, Hessian troops hired to fight against the
colonists in the American Revolution introduced this species to the east coast
of the United States in boxes of grain brought aboard ships from Europe. The
Norway rat arrived in Europe from central Asia in the sixteenth century and
subsequently spread throughout the continent. This rodent derives its common
name not because overly large populations of this species occur in Norway, but
because Norway was where early scientific descriptions of the species
originated. When local populations of the Norway rat become overcrowded, mass
migrations tend to occur. This fact most likely led to the legend of the Pied
Piper of Hamelin, who rid the town of rats by leading them into the Weser river
to drown.

Species Significance

The Norway rat is abundant in the area. Like other rodents, Norway rats
can carry diseases harmful, and even fatal, to humans such as typhoid, bubonic
plague, and spotted fever. They can also be destructive to agricultural crops
and property. White laboratory rats are a specially bred albino strain of the
Norway rat used for scientific purposes.